Coated cutting tools which also include in particular interchangeable cutting inserts and cutting bits comprise a substrate or main body with a single-layer or multi-layer coating which is deposited thereon and which serves in particular for wear protection but can also have decorative and indicator functions. The substrate usually comprises steel, carbide metal or cermet and the coating is applied using a CVD process or a PVD process. The coating is also intended to improve the cutting properties of the tool for a given application and/or to reduce tool wear.
Coatings for cutting tools which generally include outer layers with a decorative and/or indicator function are known in the state of the art.
EP 1 762 638 describes a cutting insert comprising a carbide metal substrate and a multi-layer hard material coating for wear protection and an outermost layer of ZrN which is firstly applied in a thickness of <1 μm by means of PVD and is then removed from the rake face and the cutting edge again by brushing or blasting treatment. Abrasive wear of the outer layer is an indicator of whether and how intensively a tool has already been used. DE 10 2004 010 285 and DE 100 48 899 also describe cutting tools with an indicator cover layer of golden brown TiN or also of TiC, HfC or HfN which differ in colour from the subjacent wear protection layer and make it possible to distinguish a tool which has been used from an unused tool, with the naked eye.
The outer hard wear protection layer most frequently used in relation to cutting inserts is a layer of aluminium oxide deposited using a CVD or PVD process. The decorative layer having a decorative and/or indicator function is applied thereover. A disadvantage of the known cover layers of ZrN, TiN, TiC, HfC or HfN is that the application of those layers using the PVD process requires an additional target as a source for the deposited metal component as frequently there is no source for that metal for applying the wear protection coating. In addition it would be advantageous to also have, as the decorative and indicator cover layer, a colour different from the striking golden brown colour of ZrN or TiN in order thereby also to permit colour distinguishability of different types of tool.